Large industrial hammers are, for example, percussion tools or impact vibrators and include pneumatic hammers, which are powered by compressed air, and hydraulic hammers, which are powered by a liquid.
Pneumatic hammers tend to be of smaller size and striking force than hydraulic hammers. An example of a typical pneumatic hammer is a jack hammer which is hand-held while in use, is approximately two to three feet in length and may weigh up to approximately 60 pounds. A jack hammer may deliver between approximately 900 to 1,600 blows per minute and the force of the blow is approximately 45 to 100 ft. lb. per blow.
Hydraulic hammers, by contrast, come in a variety of sizes and are usually much larger than a typical pneumatic hammer. Hydraulic hammers are often used as accessory units or attachments for construction machinery, such as excavators, loaders or other basic equipment for purposes of breaking or crushing rock, concrete or some other relatively hard material. A small hydraulic hammer may weigh approximately 265 pounds and deliver approximately 1,000 to 1,500 blows per minute with the force per blow being approximately 162 ft. lb. or 200 Joules. A very large hydraulic hammer can weigh approximately 16,000 pounds and deliver approximately 500 blows per minute with the force per blow being approximately 9,500 ft. lb. or 13,000 Joules.
Industrial hammers are generally driven by a percussion piston which moves inside a housing and alternately performs an operating stroke in a hammering direction and a return stroke in the opposite direction. During operation, the kinetic energy of the percussion piston when it strikes a tool is introduced via the tool and the tool tip into the material to be processed and the kinetic energy is converted into destructive actions. Depending on the hardness of the material to be processed, only a portion of the kinetic energy is converted to destructive action. The remaining, non-converted energy is reflected via the tool back into the percussion piston. Thus, percussion tools represent highly stressed devices that typically need frequent servicing.
Prior art testing devices have been directed towards test benches for hand operated pneumatic hammers. However, these test benches by virtue of their scale of size and component design generally are not suitable for testing the larger industrial hammers and, in particular, hydraulic hammers because of the massive size and force generated by hydraulic hammers in comparison to hand held pneumatic hammers. Most notably, these prior art devices employ an impact dissipating device that is insufficient to withstand the impact force of a large hammer and if used with a large industrial hammer the impact of the blow would not only cause the dissipating device to fail within a few blows but would also reflect the impact energy backwards through the frame of the test bench and the hammer securing mechanism so as to cause failure of the apparatus.
Examples of such prior art testing devices include, for example, U.S. Pat. No. 4,235,094 which discloses a vibration safety test bench for hand held riveting hammers wherein the riveting hammer is secured in a vertical position and the hammer is fired against a dummy work rigidly secured to the test bed and most preferably comprised of a duralumin plate. Similarly, U.S. Pat. No. 2,389,138 discloses a pneumatic hammer testing machine wherein the cutter piece of a pneumatic chipping hammer is held in place against a slab or plate of material by a pulley and weight mechanism. U.S. Pat. No. 1,576,465 discloses yet another test bench for a pneumatic rock hammer wherein the tool end of the drill is held against a testing block resiliently supported by a number of rubber blocks by a means exerting a constant force, such as a weight hanging from a chain.
Other prior art testing devices employ fluid-containing dissipating devices to receive the impact of the tool. For example, U.S. Pat. No. 4,901,587 discloses a test fixture for an air feed drill and U.S. Pat. No. 5,277,055 discloses a test stand for a hand held impact or impact-rotary tool, both of which impact the tool against a hydraulic pressurized cylinder. However, fluid-containing dissipating devices are not well suited for the repetitive and strong impact force of large industrial hammers because fluid rebounds relatively slowly and also would develop friction which would cause the unit to become hot and possibly fail.
Hydraulic hammers cannot be “dry fired” or test fired without impact against a resisting surface without causing damage to the mechanism. For this reason, it has not been possible to test fire a hydraulic hammer after servicing the unit without returning it to the field for actual in-service testing. Thus, there is a substantial need for a test bench which can accommodate the size and operating force of large industrial hammers so as to determine under test conditions whether the hammer is functioning properly.